Redis ZADD in Node.js (Detailed Guide w/ Code Examples)

Use Case(s)

The ZADD command in Redis is used to add one or more members to a sorted set, or to update the score for members that already exist. Common use cases include:

• Leaderboards or ranking systems where items are scored and ranked.
• Storing and retrieving items with some notion of priority or weight.

Code Examples

Example 1: Adding Single Member to Sorted Set

This example demonstrates how to add a single member with a score to a sorted set using Node.js Redis client.

const redis = require('redis');
const client = redis.createClient();

client.on('connect', () => {
   console.log('Connected to Redis server.');
});

const key = 'leaderboard';
const score = 50;
const member = 'user123';

client.zadd(key, score, member, (err, response) => {
    if (err) throw err;
    console.log(`Number of elements added: ${response}`);
});

client.quit();

Example 2: Adding Multiple Members to Sorted Set

This example shows how to add multiple members with their scores to a sorted set.

const redis = require('redis');
const client = redis.createClient();

const key = 'leaderboard';
const members = [
    45, 'user1',
    70, 'user2',
    55, 'user3'
];

client.zadd([key, ...members], (err, response) => {
    if (err) throw err;
    console.log(`Number of elements added: ${sponse}`);
});

client.quit();

Best Practices

• Connection Management: Ensure to close the Redis connection properly using client.quit() to free up resources.
• Error Handling: Always handle errors in callbacks to prevent unhandled exceptions.

Common Mistake

• Data Type Confusion: Ensure that the score is a number. Passing it as a string can lead to unexpected results because Redis sorts scores lexicographically when they're strings.

FAQs

Q: Can I update the score of an existing member using ZADD?
A: Yes, if a specified member is already present in the sorted set, its score will be updated, and the element repositioned accordingly.